Structural analysis of the main apse vault ofSt. George of Greeks Cathedral built c.1390 at Famagusta, Cyprus

Ata Atun

Structural analysis of the main apse vault ofSt. George of Greeks Cathedral built c.1390 at Famagusta, Cyprus

Ata
Atun

Faculty
of Engineering,

Near East
University,
Nicosia,
Cyprus

Abstract

Foundation date of the Cathedral Church of St. George of the Greeks[1] can be
dated with a high degree of probability to the end of the XIV century. This
magnificent building was built on the edge of the Greek quarter, which occupied
almost the whole of the southern end of the city of Famagusta.

The history says that this building was abandoned after 1571, as it had suffered
severely from the fire of the battery established by the Turks on the rock to
the south-east of the harbour and the marks of cannon-balls can be seen on the
walls of the apse.

The building was built so strong that it could stand any kind of battering and
to earthquake to a certain extend. In detail survey was done to find out the
building technique and materials used, including the quarry where the stones
were cut, the chemical composition and the strength of the stones and mortar
used in between. A very sophisticated structural analysis[2] was carried to find
out the strength of the main vault, its behavior and reactions to external
forces, especially to earthquake and cannon balls.

Location

Cathedral
Church
of St. George of the Greeks is situated in the
south east part of the town of Famagusta on the east cost of the Cyprus island,
located at the eastern part of Mediterranean sea.
It’s exact position is35007.2’
N, 33056.7’ E.

Figure 1: Part of the Stephan Gibellino’s gravure detailing the siege of Famagusta. Ottoman cannons
(Marked B), Cathedral Church of St.
George of the Greeks (Marked 2)

The Ottoman cannonballs battered the church were fired from;

a)
The cannons located on the rock to the
south east of the harbour.[3]

b)
The galleys outside the port.[3]

Mainly
the cannonballs fired from the cannons positioned
on the rock to the south east of the harbour
hit and damaged the Cathedral.

This
means that a single cannon ball can only penetrate to the wall but can not knock
it down. To knock down a part of
the wall,at least three cannon
balls should hit the same exact point with same velocity and same angle of
impact.

Effect of a cannonball hit to the apse vault

Impact
angle : 43.510

Vertical
component : Sin 43.51
= 0.6887 (downwards : -ve)

Horizontal
component : Cos 43.51 = 0.7250 (to the right : +ve)

F
(Impact force) = 1,539,512 kgf

Fvertical= 1,539,512 x
0.6887 = 1,060,261.91 kgf

Fhorizontal
= 1,539,512
x 0.7250
= 1,116,146.20 kgf

Figure 4
shows the dimensions and numberings of the main apse vault stones.

Figure 4 : Main
apse vault dimensions.

Assuming
direct hits to the stone no.s 27, 30 and 33, which are the most weakly covered
stones of the vault.

The
computer based static analysis results

Resisting
Moment of yellow sand stone : Rbd2/6

Where R =Compressive strength: 62.50 kg/cm2

b =
Breadth of stone =35 cm.

d = Depth
of stone = 25 cm.

MR
=62.50 x
35 x
252/6 = 227,864.58 kgf-cm

=2,278.64 kgf-m

Hit on
stone no. 27

Maximum
end force occurs on stone 46 : 1,860,774 kgf

Maximum
moment on stone 46 : -ve 105,182 kgf-m

End
moments on stone 46 : 174,727 kgf-m

Maximum
Moment Resisting Moment

No
failure

Hit on
stone no. 30

Maximum
end force occurs on stone 34 : 3,664,973 kgf

Maximum
moment on stone 34 : -ve 114,522 kgf-m

End
moments on stone 34 : 232,820 kgf-m

Maximum
Moment Resisting Moment

No
failure

Hit on
stone no. 33

Maximum
end force occurs on stone 38 : 3,495,401 kgf

Maximum
moment on stone 38 : +ve 483,969 kgf-m

End
moments on stone 38 : 389,880 kgf-m

Maximum
Moment Resisting Moment

Failure
of stone 33

Conclusion

It can be
seen from the results that;

a)When the
cannonball hit the main side walls, it could not knock down the wall fully or
partially but damage it locally, penetrating inside the outer wall 20-30 cm.
with an angle of43.510.

b)When the cannonball hit the main apse
vault stones, No.1 to 32 and No. 35 to 66, it could not knock down the stone
wholly or partially but damage the upper cover stones locally, penetrating
inside the cover 20-20 cm. with an angle of43.510.

c)When the
cannonball hit the main apse vault stones, No.33 and 34 which are the keystones
of the vault (arch) , it damaged the upper cover stones locally where the
thickness was around 10 cm. and knocked down or moved the keystones, which lead
to the partial fall down of the roof. The fall down ended where the side covers
of the vault reached to the thickness in excess of 10 + 10 cms.

My
findings lead me to the fact that the battering of the Ottoman cannonballs
managed to knock down thecentral part of the roof around the keystone and the repair of the roof
seemed very hard or impossible or was not of importance.The cannonballs hitting the side walls managed to dig holes of 20-35 cm
deep only but could not severely damage or knock down the walls. Due to the
scare look of the partially damaged vaulted roof, no body dared to stand under
it and the building was abandoned. [1]

The earth
quake which shook the whole island on 1556 [10], knock down the partially
damaged and hardly standing roof
completely.The earth quakes which
took place on 1735 [11] [12] and 1741 [13] [14]knocked down the 80% of the already shaken walls, where most of the
stones (I believe) were loose.

During
the construction years of the Suez Canal which begun on 1859 [15] and city of
Port Said (named after Said Pasha), the stones of the medieval buildings knocked
down by the earthquakes allover in the island of Cyprus were dispatched to the
area for construction purposes. This
destruction of the antiquity lasted till 1905, completion of the port of Famagusta.
[16]